Traffic engineers have many options when dealing with pedestrian traffic crossing a road. These include a simple painted crosswalk, posted pedestrian crosswalk signs and flashing beacons mounted along and sometimes in the roadway.
Where flashing beacons are used, several beacons may be arrayed around a particular crosswalk including along the roadway in both directions, on a meridian or on an island in the roadway. A complete system may have as many as 6 separate crosswalk assemblies and/or beacons around a single crosswalk.
Crosswalk beacons may often be actuated manually by a pedestrian at one of the beacons around a crosswalk. In other cases, the beacons may be triggered by a proximity or motion sensor. Whatever form it may take, the triggering event associated with a particular beacon causes that beacon to begin flashing. Where more than one beacon is arrayed around a crosswalk, it is known to use wireless communication from the triggering beacon to communicate with the other beacons in order to synchronize their flashing to that of the triggering beacon. Typically, the triggering beacon broadcasts a timing pulse used by the other beacons to cause the onset of their flashing.
Wireless crosswalk assemblies typically operate on the locally available unlicensed frequency bands such as the 902-928 MHz band in North America and the 2.4 GHz band in most of the world. However, the use of the same bands by many other devices can cause interference, such as from radio or WiFi sources such as homes, coffee shops, internet cafes, supermarkets and various businesses. As the interference affects a crosswalk signal, one of the beacons may not flash, or may not be properly synchronized, putting pedestrians and vehicular traffic at risk.
U.S. Pat. No. 7,586,421 to Witte et al. discloses a system for minimizing interference among traffic signal devices. The devices are grouped by colour or other designating indicia and each group communicates on a different frequency.
U.S. Pat. No. 5,252,969 to Kishi discloses a temporary traffic signal system wherein a pair of signal stands are installed at spaced locations. A variety of means are disclosed to synchronize the signals, including manually triggering both signals at the same time, a “parent” stand wirelessly transmitting to a “child” stand an initialization signal, and signalling by means of light or sound. The system involves two-way communication between the traffic devices of a group to allow feedback verifying that the devices are synchronized. In the event that they are not, or in the absence of a communication signal, the devices switch to a default flashing mode.
U.S. Pat. No. 7,266,141 to Goodings discloses an example of a time division multiple access frequency hopping communications system for avoiding interference.
Diggavi, Suhas, Diversity in Communication: From Source Coding to Wireless Networks, a paper apparently published before 2005, addresses the concept of diversity to ensure the integrity of communication channels, notably through the use of multiple antennas, multiple users and multiple routes.
Godavari, Mahesh and Hero III, Alfred O., Diversity and Degrees of Freedom in Wireless Communications, considers signal diversity principally from the point of view of providing redundancy of communication channels.
It is therefore a general object of this invention to synchronize the flashing of the beacons at wireless-enabled lighting or other signal assemblies with the operation of a triggering beacon.
It is a more particular object of the invention to enhance the reliability of wireless synchronization between beacons of a pedestrian-controlled crosswalk.
These and other objects of the invention will be better understood by reference to the detailed description of the preferred embodiment which follows. Note that not all of the objects are necessarily met by all embodiments of the invention described below or by the invention defined by each of the claims.